The present invention relates generally to a prosthetic foot specifically designed for amputees who require intermediate levels of strength and weight in a prosthesis. More particularly, the present invention relates to construction of a prosthetic foot and ankle joint adapted to provide a desired degree of mobility without excessive bulk.
Prosthetic feet are well known in the art, and several such feet have been designed to accomplish one or more objectives.
A useful prosthesis must simulate the operation and motion of an anatomical foot. An anatomical foot, including the ankle joint, is capable of motion around three perpendicular axes, as well as varying degrees of flexure. Specifically, the anatomical foot and ankle are capable of dorsiflexion, planiflexion, inversion, eversion, and transverse rotation. Dorsiflexion and planiflexion comprise the movement of the ball of the foot upward and downward, respectively, with respect to the heel that occurs during a normal forward step. Inversion and eversion are the twisting of the foot around its longitudinal axis, resulting in outward and inward tilting of the ankles, respectively. Transverse rotation occurs when the foot rotates with respect to the longitudinal axis of the leg, such as occurs during left and right turns of the body.
Known foot prostheses include commercial feet that are capable of all three types of rotation. Typically, however, the prosthetic joints capable of such complicated motion require bulky moving parts and are generally too heavy for some patients, including geriatric or very young patients, or other patients who suffer some degree of muscular weakness.
In addition, it is desirable for a foot prosthesis to be capable of absorbing, storing, and releasing energy. At a minimum, the prosthesis should store enough energy to return itself to a relaxed, unflexed position when the moving force is removed. Prostheses that are designed for use during athletic activities, such as running or playing basketball, are particularly efficient at energy storage and return, providing a springy step. Such energy storage is typically accomplished by the inclusion of coil springs or other reciprocating means that absorb energy on flexure and release it efficiently upon removal of the applied force. The energy-storing components that are typically used for efficient energy return can contribute significantly to the weight of the prosthesis.
In contrast, older, less mobile wearers neither need nor want a high degree of return of stored energy. Instead, it is preferable for the prostheses worn by these wearers to absorb and dissipate a portion of the energy of each flexion. This provides a more stable, cushioned step, and reduces the impact shock experienced by both the wearer and the prosthesis at each step.
Finally, it is necessary that a foot prosthesis be strong enough to support its wearer and durable enough to withstand the stresses of repeated stepping motions over long periods of time. Conventional prostheses tend to be designed for maximized strength, at the cost of added bulk and weight, making them unsuitable for intermediate wearers, who do not subject their prostheses to the same loads as more aggressive wearers, but who need a more robust prosthesis than is typically provided to low-impact users.
Hence it is desired to provide a flexible, durable prosthesis that provides intermediate energy return and a moderately damped step and yet still requires a minimal mass.
The present invention comprises a foot prosthesis having a lightweight foot portion and an attached lightweight ankle portion capable of a desired degree of rotation around each of three perpendicular axes. As used herein, the words xe2x80x9cprosthesisxe2x80x9d or xe2x80x9cfoot prosthesisxe2x80x9d refer to both the foot portion of a prosthetic foot and the ankle joint attached thereto.
Simplified construction of the foot and joint mechanism enables the present invention to be at least about 50% lighter than typical foot prostheses. The foot portion includes an integral instep, sole and dorsal member constructed of lightweight polymeric material and is designed to provide support and flexure without excessive weight. The ankle portion includes a pair of ball and socket joints that provides the desired flexibility and stability without excessive mass. Other objects and advantages of the present invention will appear from the following description.